Gas turbine engines with afterburning produce hot gas in the order of 1,500.degree. C. passing through the exhaust nozzle. Nozzle walls must therefore have sufficient strength to operate in the elevated temperature environment and must also have a reasonable life.
Nozzles therefore have been constructed with cooled underlying structure providing sufficient strength. Liners have been used to protect this underlying structure from the high temperature gas. Such liners are conventionally either catenaries of thin metal or layered louvers. While these have been cooled, provision must still be made for the thermal expansion. These previous constructions have therefore led to local bending in the high temperature environment since they were willfully left free to expand whereby these expansion could be accepted without high stresses.
Ceramic coatings may be applied to metals operating in hot environments to protect the metal surface. Such coatings are notoriously brittle. Local distortion of the liners would cause cracking and loss of the coating.
Louver and catenary construction provides walls which are not completely flat and therefore tend to cause aerodynamic losses. This is particularly so in the flaps of a 2D nozzle which must be moved to direct the gas flow.